Method and apparatus to select a parameter/mode based on a measurement during an initialization period

ABSTRACT

A power supply includes an energy transfer element coupled between an input and an output. A switch is coupled to an input of the energy transfer element. A threshold detection circuit includes in an integrated circuit coupled to measure a signal from a resistive external circuit coupled between fourth and first external terminals of the integrated circuit during an initialization period after the fourth external terminal has been charged to a supply threshold value. A regulator circuit is coupled between second and fourth external terminals of the integrated circuit. The regulator circuit is coupled to charge the fourth external terminal to the supply threshold value during the initialization period. A selection circuit is coupled to the threshold detection circuit to select a parameter/mode of the integrated circuit in response to the measured signal.

REFERENCE TO PRIOR APPLICATION(S)

This is a continuation of U.S. application Ser. No. 13/343,579, filedJan. 4, 2012, now pending, which is a continuation of U.S. applicationSer. No. 12/234,474, filed Sep. 19, 2008, now issued U.S. Pat. No.8,116,106. U.S. application Ser. No. 13/343,579 and U.S. Pat. No.8,116,106 are hereby incorporated by reference.

BACKGROUND INFORMATION

1. Field of the Disclosure

The present invention relates generally to electronic circuits, and morespecifically, the invention relates to integrated circuits in whichfunctional parameters and/or operating modes are set.

2. Background

Integrated circuits may be used for a multitude of purposes andapplications. In order to provide increased flexibility, circuitdesigners sometimes design the integrated circuits to have a variety ofdifferent operating modes and/or to have the ability to function with avariety of different operating parameters. In order for the differentfunctional parameters and/or operating modes to be set in the integratedcircuit, the integrated circuit chip is typically designed andmanufactured with an additional one or more terminals in the packagingto which additional circuit elements or signals could be coupled inorder to set or select the desired functional parameters and/oroperating modes of the integrated circuit. In the alternative, aseparate product part could be designed or manufactured with a differentintegrated circuit for each particular functional parameter andoperating mode setting designed directly into the circuitry of theintegrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive examples of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 is a schematic of an example power supply using a power supplycontrol circuit in accordance with the teachings of the presentinvention.

FIG. 2 is a block diagram of an example integrated circuit in accordancewith the teachings of the present invention.

FIG. 3 shows timing diagrams illustrating the operation of an exampleintegrated circuit in accordance with the teachings of the presentinvention.

FIG. 4 is a circuit diagram of an example power converter employinganother power supply control circuit in accordance with the teachings ofthe present invention.

FIG. 5 is a detailed internal block diagram with an example power supplycontrol circuit in accordance with the teachings of the presentinvention.

FIG. 6 is a detail circuit schematic showing a portion of an exampleintegrated circuit configuration in accordance with the teachings of thepresent invention.

FIG. 7 shows an example flowchart showing generally the operation of acontrol circuit in accordance with the teachings of the presentinvention.

DETAILED DESCRIPTION

Methods and apparatuses for an integrated circuit in which a signal atan external terminal of the integrated circuit is measured during aninitialization period of the integrated circuit to set a parameter/modeof the integrated circuit are disclosed. In one example, the terminal isused during the operation of the integrated circuit following theinitialization period for at least one other function. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. It will be apparent,however, to one having ordinary skill in the art that the specificdetail need not be employed to practice the present invention.Well-known methods related to the implementation have not been describedin detail in order to avoid obscuring the present invention.

Reference throughout this specification to “one embodiment,” “anembodiment,” “one example” or “an example” means that a particularfeature, structure or characteristic described in connection with theembodiment or example is included in at least one embodiment of thepresent invention. Thus, appearances of the phrases “in one embodiment,”“in an embodiment,” “one example” or “an example” in various placesthroughout this specification are not necessarily all referring to thesame embodiment or example. Furthermore, the particular features,structures or characteristics may be combined in any suitablecombinations and/or subcombinations in one or more embodiments orexamples. In addition, it is appreciated that the figures providedherewith are for explanation purposes to persons ordinarily skilled inthe art and that the drawings are not necessarily drawn to scale.

As will be discussed, functional parameters or operating modes of anintegrated circuit may be selected during a mode selection or functionalparameter specification setting period during the initialization periodfor an example of an integrated circuit in accordance with the teachingsof the present invention. For one example, the costs associated witheither having additional dedicated pins or external terminals on thechip package or having separate product part numbers for the purpose ofaddressing various different device functional parameter specificationsor operating modes is saved. For instance, device functional parameterspecifications may instead be selected using an existing externalterminal by measuring a signal received on that external terminal duringan initialization period of the integrated circuit.

Accordingly, selecting from a plurality of functional parameters and/oroperating modes may be provided with a single chip or integrated circuitby choosing, for example, a value of a current flowing in a resistorcoupled to an external terminal of the integrated circuit during aninitialization period of the integrated circuit. During normal operationafter the initialization period, the external terminal has a function ofsomething other than detecting the current flowing in the resistor toselect from a plurality of functional parameters, operating modes orother device characteristics. For example, the same external terminalcould be used to receive a feedback signal during the normal operationof the integrated circuit. A single pin or external terminal of anintegrated circuit can therefore be used as a feedback terminal duringnormal operation and as an input to set a parameter/mode during aninitialization period of the integrated circuit in accordance with theteachings of the present invention.

To illustrate, FIG. 1 shows a simplified schematic diagram of an examplepower supply circuit 101 in accordance with the teachings of the presentinvention. As shown, integrated circuit 104 includes a control circuit106 coupled to drive a switch 105. In the illustrated example, switch105 is coupled between an external drain terminal 107 and an externalsource terminal 108 of the integrated circuit 104. As shown, switch 105is therefore coupled to an input of energy transfer element 125 throughexternal drain terminal 107. Control circuit 106 is coupled to receive afeedback signal at external EN terminal 110 during the normal operationof the integrated circuit 104. Control circuit 106 regulates theswitching of switch 105 in response to the feedback signal received atEN terminal 110 of integrated circuit 104 to regulate energy flow frominput terminals 102 and 103 of power supply circuit 101 through energytransfer element 125 to the load 116 coupled to the output of energytransfer element 125. In the example, the feedback signal is generatedby feedback circuitry elements 121, 123 and 113, which are coupled toprovide a feedback signal responsive to the output voltage appearingacross load 116. In other examples, the feedback signal could beresponsive to a current flowing in the load 116.

In operation, when the DC input voltage 114 is first applied to theinput terminals 102 and 103, the integrated circuit 104 first charges upsupply capacitor C_(BP) 111 through an external BP terminal 109 ofintegrated circuit 104. A voltage V_(CAP) 118 across the capacitorC_(BP) 111 is increased to a threshold value that is high enough for theintegrated circuit 104 to operate correctly. In one example, the valueof this V_(CAP) 118 threshold voltage 5.8V. In order for the exampleintegrated circuit 104 to operate, a connection 170 between the Drainterminal 107 of switch 105 and the control circuit 106 is used to drawcurrent from the Drain terminal 107 to initially charge capacitor C_(BP)111. In another example, connection 170 is a connection from within thestructure of switch 105, but is shown however in the example shown inFIG. 1 as a separate connection for ease of explanation.

When the voltage across capacitor C_(BP) 111 has reached the thresholdvalue, control circuit 106 is ready to start switching switch 105 inorder to start transferring energy from input terminals 102 and 103 tothe output load 116. However, in accordance with the teachings of thepresent invention, in one example the control circuit 106 includescircuitry to delay the start of switching of switch 105 for aninitialization period. In one example, the initialization period is aperiod of 25 to 50 nanoseconds. In one example, during thisinitialization period, the control circuit 106 receives a currentflowing in EN terminal 110 through an external circuit coupled to ENterminal 110. In the example shown in FIG. 1, the external circuitthrough which current flows to EN terminal 110 includes a resistor 112.

In accordance with the teachings of the present invention, the currentflowing though EN terminal 110 during the initialization period is aparameter/mode selection signal. In the example, the control circuit 106selects a parameter/mode of the integrated circuit 104 in response tothe value of the parameter/mode selection signal. Following theinitialization period, the integrated circuit 104 starts its normaloperation where control circuit 106 switches or commutates switch 105 toregulate energy flow in the energy transfer element 125 in response to afeedback signal generated by other circuitry coupled to EN terminal 110,such as for example optocoupler 113 in FIG. 1. Integrated circuit 104therefore utilizes EN terminal 110 for an additional function aftersetting the parameter/mode during the initialization period inaccordance with the teachings of the present invention.

In one example, the parameter/mode of integrated circuit 104 that is setduring the initialization period described above is a peak thresholdlevel of a current flowing in switch 105 during the normal operation ofintegrated circuit 104. In another example, the parameter/mode ofintegrated circuit 104 that is set during the initialization periodcomprises an adjustment of a peak threshold level of current flowing inswitch 105 as a function of the value of the input voltage 114 coupledto the input of the power supply 101, during normal operation ofintegrated circuit 104.

In yet another example, the parameter/mode of integrated circuit 104that is set during the initialization period includes setting both anadjustment of a peak threshold level of current flowing in switch 105 asa function of the value of the input voltage 114 coupled to the input ofthe power supply 101 as well as a specific threshold level of current inswitch 105 at one value of the input voltage 114. Setting thresholdlevels of the peak current in switch 105 is important to set the maximumoutput power capability of the power supply 101 to suit particularapplications of the power supply 101. Setting the adjustment of peakcurrent in switch 105 as a function of input voltage 114 is important tocompensate for the effects of input voltage and maintain a substantiallyconstant maximum output power of the power supply 101 across a widerange of input voltage 114 values. This is desirable to reduce the costof many components such as the energy transfer element 125, output diode117 and output capacitor 119, which would otherwise have to be designedto cope with increased maximum output power as the input voltage 114rises.

In one example, a current flowing through a resistor 171 coupled betweenthe control circuit 106 and the input positive supply rail 102 throughexternal L terminal 172 is used by the control circuit 106 to detect thevalue of input voltage 114. The degree of peak switch current reductionwith increasing input voltage 114 can then be determined according tothe value of the signal received at L terminal 172 and the adjustmentparameter set during the initialization period described above. In oneexample where two adjustment levels are provided by control circuit 106,the peak current level in switch 105 at the highest value of inputvoltage 114 could be reduced by 10% or 20% compared to that at thelowest value of input voltage 114, depending on the value of resistor112. In other configurations, a plurality of adjustment settings of peakswitch current as a function of input voltage as well as peak switchcurrent at a specific value of the input voltage can be set.

It should be noted that in other example configurations where connection170 is not included, such as for example when control circuit 106 andswitch 105 are not part of the same integrated circuit, resistor 171could also be used to provide initial start up current from the inputpositive supply rail 102 to charge supply capacitor C_(BP) 111, whilestill benefiting from the teachings of the present invention.

In the illustrated examples, it is noted that the current flowing inresistor 112 does not influence significantly the function of ENterminal 110 during normal operation of the control circuit 106 afterthe initialization period in accordance with the teachings of thepresent invention. For instance, the measurement circuitry included inone example of control circuit 106 is designed to set thresholds for theparameter/mode selection at signal values that are an order of magnitudeor more lower than the signal values that will be present during thenormal operation of the control circuit 106 after the initializationperiod. In one example of the circuit of FIG. 1, parameter/modeselection threshold currents of 5, 10 and 20 uA are used to select fourparameters/modes during the initialization period, whereas the feedbackcurrent signal flowing in EN terminal 110 during normal operation is inthe range of 100 to 250 uA. In addition, in the circuit example of FIG.1, the current flow during the initialization period and during normaloperation is of opposite polarity, though that is not necessary tobenefit from the teachings of the present invention. It is appreciatedthat in other examples a different number n thresholds could be used toprovide a selection of n+1 parameter/modes while still benefiting fromthe teachings of the present invention.

FIG. 2 shows a simplified block diagram of an example integrated circuit204, which in one example is similar to integrated circuit 104 inFIG. 1. FIG. 3 shows example start up and initialization period timingwaveforms and will also be referred to in the following description.

The integrated circuit 204 example of FIG. 2 includes both a controlcircuit 206 and a switch 205. It is appreciated that in another example,switch 205 and control circuit 206 could be separate discretecomponents, but would still benefit from the teachings of the presentinvention. As shown in the depicted example, control circuit 206includes regulator 232 coupled to Drain terminal 207 of switch 205 andto BP terminal 209, which is the external supply terminal of controlcircuit 206. Regulator circuit 232 draws current from Drain terminal 207to initially charge capacitor 211 through BP terminal 209. Regulatorcircuit 232 outputs a UV signal 280, which goes low when the BP terminal209 reaches a threshold value at start up. In one example the thresholdvalue is 5.8V.

This is illustrated in FIG. 3 where the BP terminal 209 voltage waveform302 rises to threshold value 340 at time 348 at which time the UV signal380, which also rises with BP voltage waveform 302, goes low. It isrecognized that in an actual circuit implementation signals may go highor low depending on the polarities determined during the circuit design,while giving the same functionality. Regulator circuit 232 alsogenerates a UVset 281 signal shown as signal 381 in FIG. 3. Thisgenerates an output that is low for the duration of initializationperiod 303 and is used to set the output of threshold detection circuit233 based on the measured signal present at terminal 210 during theinitialization period 303.

In the example, the signal present at terminal 210 during theinitialization period 303 is substantially the current flowing throughresistor 212 coupled between BP terminal 209 and EN terminal 201 ofintegrated circuit 204. It is appreciated that in other examples theresistor 212 could be coupled between the EN feedback terminal 210 andany source of DC voltage while benefiting from the teachings of thepresent inventions. It is further appreciated that with an alternativeexternal circuit configuration, the signal present at terminal 210during initialization period 303 could be voltage while still benefitingfrom the teachings of the present invention. Threshold detection circuit233 outputs one or more signals 234 to be received by selection circuit231 in response to the current flowing through resistor 212 and throughEN terminal 210. Selection circuit 231 in turn outputs one or moreparameter/mode setting signals 235 to switch control circuit 230 inresponse to the one or more signals 234. In one example, the number ofsignals 235 is based on the number of parameter/modes to be set in theswitch control circuit 230. It should be noted that although not shownto simplify the diagrams, UVset 281 signal may also be used in oneexample to disable switch control circuit 230 during the initializationperiod to allow the parameter/mode selection to have taken place beforethe normal operation of integrated circuit 204 starts.

When normal operation of integrated circuit 204 does start at time 349in FIG. 3, the gate 238 of switch 205 begins receiving an active gatedrive waveform as represented by waveform 338 in FIG. 3. It isappreciated that the waveform 338 illustrated in FIG. 3 is arepresentation only. The relative high/low duty of the waveform 338would vary depending on the actual application conditions. Since UVsetsignal 381 is high for all time after time 349 in FIG. 3, subsequentselection or programming signals present at EN terminal 210 in FIG. 2are ignored by threshold detection circuit 233. As described withreference to FIG. 1, EN terminal 210 is further coupled to one or moreadditional external circuits, each of which may include one or morecomponents that may include, in one example, a feedback circuit such asan optocoupler. The one or more additional external circuits are coupledto provide one or more signals at the EN terminal 210 at times otherthan the initialization period 303, to provide at least one additionalfunction for the integrated circuit 204 after the initialization period303 is complete. In one example, the one additional function is afeedback terminal function illustrated in FIG. 2 by the coupling of optocoupler 213 coupled to the EN feedback terminal 210.

FIG. 4 shows another simplified example power supply schematic includinga simplified block diagram of an integrated circuit 404 including acontrol circuit 406 and, in the example shown, three switches 405, 463and 464. In one example integrated circuit 404 could be used in apersonal computer power supply where the system requires both main andauxiliary or standby power converters. Example control circuit 406combines the control circuitry for both main and standby converters. Inthe example, power switches 463 and 464 are coupled to the main powerconverter transformer 465, the output of which is coupled to generateMain DC OUT voltage 488. The main converter output voltage 488 iscoupled to optocoupler 468 to generate a feedback signal at feedbackterminal FB 485 in order to control the value of output voltage 488.

In the example, power switch 405 is coupled to the standby powerconverter transformer 466, the output of which is coupled to generatedStandby DC OUT voltage 489. The standby converter output voltage 489 iscoupled to optocoupler 467 to generate a feedback signal at feedbackterminal EN 410 in order to control the value of output voltage 489.

In the example of FIG. 4, threshold detection circuit 433 is coupled toreceive signals at both terminals 410 and 485 during the initializationperiod of integrated circuit 404 in accordance with the teachings of thepresent invention. In this way parameter/modes can be set for either orboth the main and standby converter control. In the example therefore,both resistors 412 and 462 are selected to set parameter/modes duringthe initialization period in accordance with the teachings of thepresent invention. However, the operation of control circuit 406 duringthe start up and initialization period shares many aspects with thedescriptions of the more simple control circuit examples discussed inFIGS. 1, 2 and 3. In the example, therefore signals at both terminals410 and 485 are measured by threshold detection circuit 433 during aninitialization period that is started when regulation circuit 432 hascharged BP capacitor 411 to a threshold value when input voltage 414 isfirst introduced to the input of power supply 401. In one example,during the normal operation of integrated circuit 404, FB terminal 485has a substantially high voltage relative to source potential 408 thanEN terminal 410. For this reason, in one example, during theinitialization period of integrated circuit 404, the voltage of FBterminal 485 relative to source potential 408 is reduced by the actionof circuitry internal to integrated circuitry 404 not shown. Thisreduction in the voltage of terminal 485 reduces the influence ofleakage current flow in opto coupler 468 that could otherwise influencethe accuracy of the measurement of the signal at terminal 485 during theinitialization period of integrated circuit 404.

During the initialization period, threshold detection circuit 433outputs one or more signals 434 coupled to selection circuit 431 inresponse to the signals at terminals 410 and 485. Selection circuit 431outputs one or more parameter/mode selection signals 435 to switchcontrol circuit 430 in response to the one or more signal 434 fromselection circuit 431. In common with the control circuit of FIG. 2,timing signals are generated to ensure that initialization andparameter/mode selection is complete before the switch control circuit430 initiates switching of switches 405, 463 and 464. These signals arenot shown in FIG. 4 to simplify the diagram. In common with the circuitof FIG. 1, the integrated circuit 404 of FIG. 4 is coupled to thepositive supply voltage rail 402 through a resistor 471 to L terminal472. The current flowing in resistor 471 is a function of the inputvoltage 414 and this signal can therefore be used to adjust a peakcurrent threshold value in all or some of switches 405, 463, 464. In oneexample, one of the parameter/modes that can be selected through thechoice of resistors 412 and 462 is an adjustment of a peak currentthreshold level of currents flowing in one or more of the switches 405,463 and 464, as a function of the input voltage 414 in accordance withthe teachings of the present invention.

FIG. 5 shows another block diagram of an example power supply controlcircuit in accordance with the teachings of the present invention. Thecontrol circuit of FIG. 5 shares many aspects of the block diagram ofFIG. 2. At start up, the regulator circuit 532 draws current I_(charge)561 from the Drain terminal 507 of switch 505, to charge the capacitor511 coupled to BP terminal 509. When the under voltage threshold ofcomparator 571 is reached, the output signal 580 goes high. However,circuit 595 generates an initialization pulse that temporarily disablesswitching of switch 505 while the threshold detect circuit 533 detectssignal 534.

Signal 534 is generated by current mirror 599, which mirrors current 590flowing into the EN terminal 510 through external resistor 512 duringthe initialization period. In other examples, signal 534 could be madeup of a plurality of signals generated from a plurality of currentmirror outputs as will be shown in the example illustrated in FIG. 6.Threshold detect circuit 533 outputs signals 535, which are coupled toparameter/mode selection circuit 531. Parameter/mode selection circuit531 provides outputs to the remaining circuitry in the schematic of FIG.5 that collectively make up the switch control circuitry of controlcircuit 501.

In the example illustrated in FIG. 5, the outputs of parameter/modeselection circuit 531 include signal 553 to adjust a current limit levelfor setting a peak current threshold for current flowing in switch 505current, signal 557 to adjust a frequency of an internal oscillator 567and signal 555 to adjust a thermal shutdown protection threshold ofcircuit 565.

In the example shown in FIG. 5, the example control circuit 501 uses anon/off mode of control in which cycles of the switch 505 are skipped orenabled to regulate energy delivery in the power supply circuit in whichis it used. As such, the frequency adjust signal 557 sets a maximumswitching frequency of the switch 505 when no cycles are skipped atmaximum output power conditions. It is appreciated that any parametersor modes of operation could be set using the teachings of the presentinvention and that the circuits shown in FIG. 5 illustrate just a fewexamples for explanation purposes.

FIG. 6 shows a detailed schematic 601 of a portion of one example ofcontrol circuit in accordance with the teachings of the presentinvention such as the control circuit 406 of FIG. 4. The discussionbelow is focused on specific aspects of the example circuit illustratedin FIG. 6 in accordance with the teachings of the present invention. Inthe illustrated example, EN node 610 and BP node 609 are coupled toexternal terminals or pins of the control circuit and resistor 612 is anexternal resistor coupled between the pins to provide the parameter/modeselection signal discussed above with reference to FIGS. 1 to 5.

During an initialization period of the control circuit 601 in FIG. 6,the current flowing through resistor 612 is mirrored by current mirrorcircuit 643 and applied to threshold detection circuit 633 throughsignals 634 flowing through transistors 675, 676 and 677. When signalUVset 681 goes low, the outputs of threshold detection circuit 633 areset. In one example, this is similar to UVset signal 281 in FIGS. 2 and3. The output signals 634 from threshold set circuit 633 are coupled toinputs of selection circuit 631. When UV signal 680 is high at the startof the initialization period the outputs 664 and 665 of selectioncircuit 631 are also held low by the action of NOR gates 688 and 687.The description below describes how the signal generated by theoperation of one of the current mirror transistors 676 in current mirrorcircuit 643, sets the output of NOR gate 687. It will be appreciatedthat similar explanations can be applied to the signals generated byother current mirror transistors 675 and 677.

In the illustrated example, transistor 682 is a current source, which inthe example is a 10 uA current source. If the current flowing intransistor 676 exceeds 10 uA, the voltage across transistor 676 istherefore low providing a low input signal an input of NOR gate 684.When UVset signal 681 goes low, for example at time 348 in FIG. 3, theinverse of the polarity of the voltage at the Drain of transistor 676 ispassed through NOR gate 684 for the duration of the period for whichUVset signal 681 remains low, which in one example is for the durationof initialization period 303 in FIG. 3. If the Drain of transistor 676is low during this initialization period, the signal 683 therefore goeshigh at the output of NOR gate 684. This output high signal is appliedto an input of NOR gate 686. As described above, the output of NOR gate687 is held low while UV signal 680 is high and output of NOR gate 686is therefore the inverse polarity of signal 683. When UV signal 680 goeslow, for example at time 348 in FIG. 3, output 665 therefore follows theinverse polarity of the output of NOR gate 686, which from the abovedescription was until this time the inverse of the polarity of signal683. In the example therefore, the output signal 665 takes on thepolarity of signal 683 during the initialization period, which in oneexample could be period 303 in FIG. 3. The outputs of selection circuit631 are applied to the input of a switch control circuit, which is notshown in FIG. 6, but could in one example be similar to switch controlcircuit 430 in FIG. 4 or switch control circuit 230 in FIG. 2. In theexample, two levels of a peak current threshold of a switch coupled tothe control circuit 601 are set depending on the polarity of outputsignal 665. In addition, output signal 664 sets one of two levels of anadjustment of the peak current threshold as a function of a voltageinput to the power supply in which control circuitry 601 is used inaccordance with the teachings of the present invention.

It is appreciated that circuitry similar to that shown in FIG. 6 couldbe employed coupled to FB terminal 485 of integrated circuit 404 in FIG.4 to provide functionality similar to that described above withreference to circuitry 601 in FIG. 6.

In the descriptions above, it is noted that the function of the terminalduring normal operation of the integrated circuit has been as a feedbackterminal for explanation purposes. It is appreciated however that anyterminal could be used that can receive a signal during aninitialization period of the integrated circuit to set parameter/modesof the integrated circuit and then subsequently receive another signalduring the normal operation of the integrated circuit to perform anotherfunction in accordance with the teachings of the present invention.

FIG. 7 shows an example flowchart 700 showing generally the operation ofa control circuit in accordance with the teachings of the presentinvention. As shown, operation starts at block 701 and the circuit ispowered up at block 702. At block 703 a decision is made as to whetherthe control circuit is in an initialization period. If so, then at block704 the value of a signal received at one of the terminals of thecircuit is detected and at block 705 a parameter/mode of the circuit isset based on the value of the signal detected in block 704. Processingthen proceeds from block 705 to block 706, where the circuit operatesnormally using the terminal for an additional function during normaloperation of the circuit. Block 706 is also entered if, at block 703, itis determined that it is not an initialization period of the circuit.

The above description of illustrated examples of the present invention,including what is described in the Abstract, are not intended to beexhaustive or to be limitation to the precise forms disclosed. Whilespecific embodiments of, and examples for, the invention are describedherein for illustrative purposes, various equivalent modifications arepossible without departing from the broader spirit and scope of thepresent invention. Indeed, it is appreciated that the specific voltages,currents, frequencies, power range values, times, etc., are provided forexplanation purposes and that other values may also be employed in otherembodiments and examples in accordance with the teachings of the presentinvention.

These modifications can be made to examples of the invention in light ofthe above detailed description. The terms used in the following claimsshould not be construed to limit the invention to the specificembodiments disclosed in the specification and the claims. Rather, thescope is to be determined entirely by the following claims, which are tobe construed in accordance with established doctrines of claiminterpretation. The present specification and figures are accordingly tobe regarded as illustrative rather than restrictive.

What is claimed is:
 1. A power supply, comprising: an energy transferelement coupled between an input and an output of the power supply; aswitch coupled to an input of the energy transfer element; a thresholddetection circuit included in an integrated circuit coupled to measure asignal from a first resistive external circuit coupled between a fourthexternal terminal of the integrated circuit and a first externalterminal of the integrated circuit during an initialization period afterthe fourth external terminal has been charged to a supply thresholdvalue; a regulator circuit coupled between a second external terminal ofthe integrated circuit and the fourth external terminal, the regulatorcircuit coupled to charge the fourth external terminal to the supplythreshold value during the initialization period of the integratedcircuit; and a selection circuit coupled to the threshold detectioncircuit to select a parameter/mode of the integrated circuit in responseto the signal measured from the first resistive external circuit duringthe initialization period of the integrated circuit.
 2. The power supplyof claim 1 where the switch is included in the integrated circuit and iscoupled between the second external terminal and a third externalterminal of the integrated circuit.
 3. The power supply of claim 2wherein the parameter/mode comprises a peak current threshold level of acurrent flowing in the switch.
 4. The power supply of claim 2 whereinthe parameter/mode comprises a parameter that sets an adjustment of apeak current threshold level of a current flowing in the switch inresponse to an input voltage of the power supply.
 5. The power supply ofclaim 4, wherein the parameter/mode further comprises a peak currentthreshold level in the switch at a certain value of the input voltage.6. The power supply of claim 1 wherein the fourth external terminal ofthe integrated circuit comprises a supply terminal of the integratedcircuit such that the first resistive external circuit is coupledbetween the supply terminal of the integrated circuit and the firstexternal terminal of the integrated circuit.
 7. The power supply ofclaim 1 wherein the parameter/mode that is selected by the selectioncircuit during the initialization period of the integrated circuitcomprises an operating frequency of the integrated circuit.
 8. The powersupply of claim 7 wherein the operating frequency of the integratedcircuit is a maximum operating frequency of the integrated circuit. 9.The power supply of claim 1 wherein the signal measured from the firstresistive external circuit is a current.
 10. The power supply of claim 1wherein the first external terminal of the integrated circuit is furthercoupled to receive a feedback signal during normal operation of thepower supply at times other than the initialization period of theintegrated circuit.